The present invention relates to an inkjet recording apparatus, and more particularly to an inkjet recording apparatus having a so-called linear inkjet head provided with continuously arranged ink ejecting nozzles in a width direction of a recording medium.
Recently, inkjet printers have been widespread since they generate less noise, and standard paper can be used as recording medium. A conventional inkjet printer typically employs an inkjet head which sweeps in a width direction (main sweeping direction) of the recording medium, which moves relative to the inkjet head in a direction (auxiliary sweeping direction) perpendicular to the moving direction of the inkjet head to form a two-dimensional image on the recording medium. Such an inkjet head is referred to as a serial type inkjet head.
In such an inkjet printer, since the inkjet head moves, an image forming speed is limited to a certain level, and is difficult to meet a recent demand of high-speed imaging. To meet such a demand, usage of a linear inkjet head attracts attention. The linear inkjet head is provided with a plurality of ink ejecting nozzles arranged in a line, which extends in a width direction (i.e., the main sweeping direction) of the recording medium. Typically, the linear inkjet head is fixed at a position, while the recording medium is driven to move at a high speed in the auxiliary sweeping direction, so that the imaging speed is greatly accelerated.
Incidentally, ink resides at the ink ejecting nozzles of the inkjet head tend to dry easily since it is exposed to the air. Therefore, before a printing job, and may also be during the printing job, a flushing operation for forcibly removing the residual ink at the ink ejecting nozzles may be performed. When the inkjet head is a serial type, a flushing position is defined, which is a position outside an imaging area for the recording sheet, and the flushing operation is performed with the inkjet head located at the flushing position.
However, when the inkjet head is a linear head, it is difficult to perform the flushing operation by moving the inkjet head to a position outside the imaging area of the recording medium since a wide space for allowing the inkjet head to move and a highly accurate driving mechanism to move the inkjet head between the operable position and a flushing position should be provided. A method in which a member that collects the forcibly discharged ink is moved to the inkjet head at every flushing operation has once been suggested. However, such a method requires a space and a mechanism for moving the ink collecting member. Further, it takes time to execute such a flushing operation, and is not suitable for the purpose of improving the imaging speed.
Japanese Patent Provisional Application No. 2001-71521 shows an exemplary configuration to cope with such a problem. In this publication, a rotatable cylindrical member having a slot, which is through-bored along the diameter and is elongated in the axial direction of the cylindrical member, is provided immediately below an inkjet head. Further, an ink absorbing member is provided so as to face the inkjet head with the rotatable cylindrical member therebetween. When the flushing operation is performed, the rotatable cylindrical member is rotated so that the inkjet head and the ink absorbing member face each other through the slot, and the ink discharged by the inkjet head is absorbed by the ink absorbing member.
Another configuration disclosed in Japanese Patent Provisional No. HEI 63-60850 includes an ink absorbing member which faces the nozzles, and a retractable platen is provided between the inkjet head and the ink absorbing member. In this configuration, when the flushing is performed, the platen is retracted from the position between the nozzles and the ink absorbing member so that the ejected ink is absorbed by the ink absorbing member.
Even in the configurations disclosed in the above publications, operations dedicated only to the flushing operation are required, and it may take several seconds to perform the flushing operation. If, for example, an imaging speed of an inkjet printer is 180 sheets/minute, and a flushing operation is performed at every completion of imaging on a sheet, the imaging speed is decelerated to 20 sheets/minute due to the flushing operations. Thus, image formation speed is fast but the effective imaging speed including the flushing operation cannot be sufficiently accelerated.
As such, an improved inkjet recording apparatus which can execute the flushing operation without decelerating the recording speed has been desired.